It's not that chrome makes the bolt harder, it's steel on aluminum either way. It's that the chrome builds up the outer surface and makes the carrier/ bolt larger. This increased size has to mate to the upper and barrel extension and cause wear and binding until the upper re-mates.

The only benefit that anyone agrees on is that the chrome plating makes the parts easier to clean, since you can see the fouling.

Food for thought.

I once thought that I had all the answers, but after consorting with the "Magic 8 Ball", I have found it to be "Doubtable Not So".

The chrome plating may build up the surface a little. But if it is done correctly, by a place that specializes in firearm plating,(NOT the local car bumper plating shop) there shouldn't be a problem.Hard Chrome plating also has the benefit of being self lubricating. I seriously doubt that it would be enlarged enough to cause excessive wear on an upper. It does have the advantage also of not letting the powder and carbon build up stuck too badly to the chrome surface.

The bolt was hard chromed by a local machine shop. The head of the shop is a long time shooter and understood the process needed for ther bolt.

I had 2 bolts and the first was chromed individually and then the key was assembled. The extractor and ejector were hard chromed and then assembled. So far the test firing show no undue rubbibg on the upper and there have been no problems with feeding and extraction. I've shot approx 500 rounds during the test firing.

Cleaning was much easier!!!!!!

After I finish the break in period and everything continues smoothly, I plan on having my other bolts hard chromed also. The shop foreman also suggested I consider hard chroming the disconnector, trigger sear and the parts of the hammer that interface with these parts. Supposedly the self lubricating qualities of hard chrome would help the firing mechanism and the hard chrome would reduce wear.

The Army stopped using chromed bolt carriers in deployable units back in the 1970s, because it was found they cause excessive wear in upper receivers. Chromed bolt carriers are relegated to training units. Mil-spec bolt carriers are chromed inside where the rings go, but not on the outside.

Chrome bolts are allowed but they're not mil-spec. From what I've read, they seem to be prone to breakage.

I was told (and I've never served)the Army told the troops they stopped using the chrome bolts because the enemy could see the glint. But I was told the real reason was cost.
And they continued using the chrome bolts for training rifles because they get more wear and tear that issue rifles. And that seems to make sense. Why would the Army use chrome bolts in the rifles subjected to more use if the chroem bolts caused more wear?
I dunno. I guess I'll find out after many more rounds.
Big_Bear, did you hear why they are more prone to breakage?

Chromebolt, chrome bolts can be brittle if the chroming process isn't done just right. Forest, a member of this board, posted a good writeup [url=http://www.alpharubicon.com/leo/ar15sforserious.htm]here[/url], where he mentioned that he knew a person who was on his THIRD chrome bolt. The first two broke, one after 200 rounds. HTH